For various reasons, it is often desired to effect a different solids content of a composition from the solids content normally in that composition. Generally speaking, processes for effecting such different solids content can be broadly classified in two categories, i.e. thermal processes and mass transfer processes. Thermal processes involve heating the composition to a temperature where the non-solids of the composition are either evaporated or distilled. Such processes can alter the solids content of the composition such that the resulting composition is in the form of an increased solids content composition or in the form of a dried composition, where at least a portion of the non-solids content of the composition is removed. Typical thermal processes include heat evaporization, oven drying, and spray drying.
On the other hand, those processes which involve a mass transfer do not normally include a thermal process, or, at least, includes a thermal process with substantially less thermal separation than the typical thermal processes. Among the known mass transfer processes are ultrafiltration, centrifugal separation, and freeze drying.
As examples of the foregoing, milk may be concentrated by vacuum pan evaporation to produce evaporated milk. This process involves heating and is, in part, therefore a thermal process. Soluble coffee can be made from a thermal process, e.g. spray drying, or it can be made from a mass transfer process having a minor thermal process involved, e.g. freeze drying. Tomato paste can be made from a thermal process involving a low temperature spray drying.
As another example of this difficulty in the art, some juices may be effectively concentrated by thermal processes and other juices may not. For example, tomato juice can be effectively concentrated by a thermal process, but orange juice concentrated by a thermal process is of decidedly inferior quality than fresh orange juice. Thus, even with compositions as closely related as the various fruit juices, there is little or no predictability in the art as to which of the many concentration processes will be effective for satisfactorily concentrating a particular juice.
All of these various processes for effecting a different solids content of the composition to be treated have their own special advantages and disadvantages. Many compositions suffer deleterious effects when subjected to a thermal process or to a mass transfer process involving a thermal step. For example, spray dried soluble coffee has a distinctly different taste than freshly brewed coffee, since the thermal spray dry process removes some of the flavor and aroma of the coffee. Freeze drying coffee retains more of the flavor and aroma of brewed coffee, but even in the freeze drying, some loses of flavor and aroma result. On the other hand, tomato paste cannot be satisfactorily produced by a freeze drying process, since tomato juice is unstable under the freezing conditions. Thus, tomato paste is made with a thermal spray dry process, but which process is operated at lower temperatures.
Accordingly, when it is desired to effect a different solids content in known compositions, the art has a wide variety of possible processes from which to choose, with many variations thereof. However, it is usually most unpredictable as to which of these processes, if any, will produce a product of satisfactory characteristics. Under these circumstances, the art has not been able to predict which process, if any, is amenable to effecting a different solids concentration in a particular composition, and the art has been forced to extensive and expensive experimentation to find which process, if any, of all the known various processes and modifications thereof is amenable to satisfactorily effecting such different solids concentration in the composition of interest.
The same problem in the art has existed in connection with effecting different solids concentrations in liquid dairy products. For example, skim milk or whole milk may be concentrated in a thermal process to produce an evaporated milk. However, as is also known, evaporated milk has a taste, texture and mouth feel, either in the concentrated form or in the reconstituted form (reconstituted with water), which is substantially different from the taste, texture and mouth feel of fresh milk. In addition, the functionality of the evaporated milk, as opposed to fresh milk, is changed during that thermal process. For example, evaporated milk cannot be used in certain types of cooking and baking, as opposed to fresh whole milk. As another example, evaporated whole milk, while having fat contents similar to cream, cannot be effectively whipped into a whipped topping, similar to whipped cream.
On the other hand, milk can be subjected to mass transfer concentration processes, such as ultrafiltration, which do not involve a thermal step; but ultrafiltration removes a number of components from the milk, and the product which results therefrom, either in its concentrated form or reconstituted form, is substantially different from milk.
The problem of effecting a different solids content in liquid dairy products is even more difficult than the problem associated with the art in general. Liquid dairy products, such as milk, are emulsions, and, hence, are affected by the various known concentration processes in manners substantially different from other compositions which are solutions and/or suspensions, such as brewed coffee and juices. Further, milk has a delicate balance between the emulsions of the butterfat, the various proteins, and the ash (composed primarily of minerals). In addition, milk contains substantial amounts of lactose, and that lactose cooperates in this delicate balance. As a result thereof, even in known methods of concentrated milk, e.g. in the evaporation process, there is a definite upper limit as to the amount of concentration which can be achieved without disturbing that balance and rendering the product unsatisfactory. Generally speaking, for acceptable products, milk can only be evaporated to the extent that the original volume can be reduced to somewhere only about one half without most undesired effects being experienced. In other words, with, for example, evaporation and starting with a solids content of between about 5 and 10%, the solids content of the evaporated milk can only be about 10 to 20%.
As a result thereof, considerable effort has been extended in the art for finding processes for satisfactorily concentrating liquid dairy products. Heretofore, no such process has been sufficiently satisfactory to yield commercially viable concentrated liquid dairy products, other than the evaporation process. In this regard, concentration should be distinguished from drying, such as spray drying, where satisfactory spray dried non-fat milk solids can be produced.
It would be, therefore, of considerable advantage in the art to provide processes for concentrating liquid dairy products where the processes do not substantially adversely affect the taste, texture and mouth feel of the concentrated liquid dairy product, or the reconstituted form thereof, and which can be conveniently and economically operated.